This invention relates to a valve nozzle device used in conjunction with an injection molding machine.
Heretofore a device has been used including a nozzle and a valve that controls the operation thereof, and such a device is hereinafter termed a valve nozzle device.
FIG. 1 illustrates an example of the valve nozzle device which is coupled with a material heating cylinder 1 of an injection molding machine. In the cylinder 1, a material for instance a plastic resin is heated to a melted state, and while the weight of the resin being measured, the melted resin is forced by a feed screw 2 provided in the cylinder 1 into a passage 3 and then into a chamber 4 both provided in the valve nozzle device.
The device further comprises a needle valve 5 which is urged by a spring 7 toward a nozzle 6 formed at one end of the chamber 4. When the pressure of the plastic resin in the chamber 4 rises beyond a predetermined value, the needle valve 5 retracts against the force of the spring 7 to open the nozzle 6.
The needle valve 5 is passed through a sheath or torpedo 9 rigidly supported by spiders 8 of the valve nozzle device. However, the rigid support of the spiders 8 inevitably restricts the passage 3 formed through the spiders 8 as shown in FIG. 2 wherein the passage 3 is divided into a number of round holes 3a of comparatively small diameters or as shown in FIG. 3 wherein the passage 3 is formed into two oval holes 3b, thus resulting in a disadvantage of increasing the pressure loss in the passage 3.
Another valve nozzle device has also been known, the device having a number of valve nozzles (two in the example shown) as shown in FIGS. 4 and 5.
The device is provided with a heating cylinder 11 containing a feed screw 12 as described with reference to FIG. 1. The valve nozzle device generally designated by a numeral 13 has a first central passage 14 receiving the melted plastic resin delivered from the heating cylinder 11. The plastic resin is then passed through a second passage 15 extending substantially at right angles with respect to the first passage 14 into valve chambers 16a and 16b, and then injected into metal molds (not shown) through nozzles 17a and 17b formed in communication with the valve chambers 16a and 16b, respectively. Needle valves 18a and 18b provided adjacent to the nozzles 17a and 17b are urged by springs 19a and 19b normally close the nozzles 17a and 17b, respectively. However, when the pressure of the plastic resin in the valve chambers 16a and 16b exceeds a predetermined value, the needle valves 18a and 18b are moved against the forces of the springs 19a and 19b to positions opening the nozzles 17a and 17b, respectively.
With the above described construction of the conventional multivalve nozzle device, since the second passage 15 extending substantially at right angles with respect to the first passage 14 is in a plane including the needle valves 18a and 18b as best illustrated in FIG. 5, stagnation or deposition of the plastic resin is caused at positions A and B shown in FIGS. 6 and 7. The stagnation or deposition of the plastic resin causes a pressure loss in each valve chamber. Although the deposition of the plastic resin may be more or less reduced by selecting the positions of the needle valves 18a and 18b suitably with respect to the second passage 15, heretofore the complete elimination of the stagnation or deposition has been impossible.